The invention relates to a system of manufacturing and, more particularly, a method and system for improving the quality of the assemblies and sub-assemblies of an automobile.
A conventional automobile assembly line produces a variety of sub-assemblies that are integrated to form a complete vehicle. For example, typical modern vehicles, such as a sedan, have a body-in-white which is comprised of a front or engine room sub-assembly, a passenger cell sub-assembly and a trunk or rear sub-assembly. Typically, a front sub-assembly will be attached to the passenger cell sub-assembly at a first assembly station on the main assembly line. The front and passenger cell sub-assemblies are usually affixed to each other by spot welds or bolts. The rear sub-assembly is then attached to the front/passenger cell assembly at a second assembly station on the main assembly line.
The sub-assemblies themselves are typically produced on a sub-assembly line, which may or may not be at the same location as the main assembly line. A sub-assembly is typically produced by affixing, typically by spot welds, a number of components, parts or pieces (which terms, hereinafter, will be used interchangeably). For instance, the front or engine room assembly typically comprises left and right front housings (which include the left and right wheel wells and shock towers), left and right frame rails, a fire-wall or dashboard component and a radiator cradle. In a typical sub-assembly line, separate left and right front fender sub-assemblies, typically comprising the front frame rails and front housings, are formed by placing the individual components into a jig at a first weld station and spot welding these components to form separate left and right fender sub-assemblies. The left and right front fender sub-assemblies are then joined together by a dashboard component to form a U-shaped structure (when viewed from overhead). This U-shaped structure is then moved to another sub-assembly line station for the installation of the radiator cradle. Further components which form part of the engine room or front sub-assembly may also be added.
Conventionally, the components which form the sub-assemblies are themselves typically comprised of a number of folded, stamped, rolled, extruded, or hydroformed pieces which are affixed to each other to form the component. These components may be produced off-site by the vehicle manufacturer or by a supplier.
In conventional assembly lines (including sub-assembly lines), many of the assembly steps require parts to be physically stacked on top of one another and then secured to each other by, for example, welds or bolts. Each of these components is formed with a certain accuracy or tolerance. That is, a particular component, and any point on that component, is typically required to have, or be located at, certain dimensions, within a specified tolerance, (i.e.xc2x11 mm, for example). If a component to be affixed references a point or another component, the reference point also having a dimensional tolerance, the tolerance in the assembly formed by these components will be also be xe2x80x9cstackedxe2x80x9d together. That is the dimensional tolerance of the first component will be added, to some degree, to that of the second component. As more components are affixed to the assembly which reference additional points, the tolerances of the individual points are xe2x80x9cstackedxe2x80x9d to create a larger total tolerance for the xe2x80x9cstackedxe2x80x9d component.
The positioning of these components spatially and relative to one another and prior to fixation is typically accomplished through the use of jigs. By way of explanation, a jig typically has pins and templates, (or location devices, such as cavities, for example) to receive parts, and clamps, to maintain parts in position prior to welding. However, a jig typically allows some play in the positioning of the parts prior to clamping (such as xc2x10.3 mm). As a result, the use of additional jigs conventionally incurs a quality penalty. That is, for each jig used, an addition positional tolerance is conventionally incurred. As a result, in a conventional assembly line, each additional jig used to spatially hold parts together prior to welding causes the positional tolerance of that jig to be added, in some degree, to the total tolerance of the final product. Accordingly, it becomes evident that an increase in the number of components whose positional and dimensional tolerances are stacked causes the total manufacturing tolerance to increase. It is evident that as the number of xe2x80x9cstackingxe2x80x9d processes increases the total manufacturing tolerance can become quite substantial.
As is well known in the automotive industry, the demand for higher quality vehicles at a lower cost is increasing. It is not uncommon for customers to demand quality tolerances for visibly apparent quality measures, such as body panel gaps, of less than 3 mm. However, it is not uncommon for some assembly processes to have twenty or thirty welding stations using twenty, or more, positioning jigs.
Accordingly, it is desired to improve the manufacturing method by reducing the overall or total tolerance in sub-assemblies and vehicle assemblies.
According to an aspect of the invention, there is provided an assembly line, comprising: an initial station with means for forming a substantially rigid initial structure from a plurality of components; at least one additional station downstream of said initial station, each of said at least one additional station including: referencing means for referencing or positioning additional components relative to said initial structure; and affixing means for affixing each additional component to said initial structure at a position referenced by said referencing means.
According to another aspect of the invention, there is provided an assembly line, comprising: an initial station with means for forming a substantially rigid initial structure from a plurality of components; a plurality of additional stations downstream of the initial station, each of the plurality of additional stations including: referencing means for referencing additional components to the initial structure; and affixing means for affixing each additional component in abutting relation to the initial structure at a position referenced by the referencing means.
In a particular case, the assembly line may include a plurality of additional stations which are serially arranged. In another particular case, the plurality of components forming the initial structure may be positioned relative to a reference point on one of the plurality of components. In still another particular case, the assembly line may be for manufacturing vehicle sub-assemblies. In yet another particular case, the referencing means may be one or more of: a jig; a vision system; and a handling robot. Similarly, the means for affixing the additional components may be one or more of: welding, adhesives, bolts, rivets, joints and fasteners. Still further, the assembly line may include a plurality of sub-assembly lines, based on the assembly line of the embodiments, for the assembly of a plurality of sub-assemblies, and further include assembly means for referencing and affixing the manufactured sub-assemblies to one of the initial structures manufactured on one of the plurality of sub-assembly lines.
According to another aspect of the invention, there is provided an assembly line for manufacturing an assembly from a plurality of components. The assembly line comprises: an initial station for forming a substantially rigid initial structure from selected components of the plurality of components; at least one additional station, downstream of the initial station, that comprises: a component positioner for positioning non-selected components of said plurality of components relative to a reference point defined on said initial structure; and an affixer for affixing said non-selected components to at least one of said initial structure and another of said non-selected components.
In a particular case according to this aspect of the invention, the plurality of components may be a plurality of sub-assemblies. Further, the assembly line may be for manufacturing vehicle assemblies.
In the embodiments according to the invention, the formation of an initial substantially rigid structure with a reference point significantly reduces the amount of total manufacturing tolerance introduced during the assembly process as the assembly is transported from processing station to processing station. Moreover, the amount of dimensional tolerance in the manufacture is reduced by reducing the number of independent reference points used.